Technical Field
The present invention relates to a kneading apparatus for kneading an object to be kneaded, and more specifically to a kneading apparatus in which two rotary shafts each having a plurality of paddles as stirring members provided on the external periphery thereof are disposed parallel to each other and caused to rotate in opposite directions to knead an object to be kneaded with the paddles.
Background Art
Conventionally, such a kneading apparatus (mixer) has been used, for example, in mixing dehydrated sludge, incinerated or collected dust, cement and other types of dust mixed with a solidifier, or fertilizer and other types of powdery or granular material, and also in kneading powdery or granular material with liquids added thereto.
This type of kneading apparatus is disclosed in Patent Document 1, in which a plurality of paddles is erected and arranged spirally. First and second rotary shafts are caused to rotate in opposite directions to convey an object to be kneaded in a direction along the two rotary shafts while being stirred and kneaded by the paddles. The two rotary shafts are rotated such that the distal ends of the paddles come in proximity to the external peripheral surface of the facing rotary shaft. Causing the two rotary shafts to rotate at unequal speeds causes the paddles of the two rotary shafts to scrape off the kneaded object that has adhered to the external peripheral surface of the other rotary shaft, thus performing self-cleaning. The paddles of the two rotary shafts are all attached at a specified incline of about 45°, for example, relative to the center axes of the rotary shafts so that the kneaded object is pushed in the conveying direction in accordance with the rotation of the rotary shafts during kneading.
Patent Document 1: Japanese Laid-open Patent Application No. 1987-157113
However, the configuration of the conventional kneading apparatus has the following problems.
Although not a problem in the case of mixing powdery or granular materials, “lumping” sometimes occurs in cases of kneading a powdery or granular material with a liquid. The liquid aggregates and forms clumps in part of the powdery or granular material depending on the blend ratio or at times such as when the liquid is highly viscous. When lumping occurs, it is not easily resolved, and in some cases uniform kneading of the entire material will be impeded.
In an arrangement in which self-cleaning is performed, as is described in Patent Document 1, the facing paddles of the two rotary shafts repeatedly move toward and away from each other with every rotation of the rotary shafts. When the facing paddles are nearest to each other, the kneaded object can be squeezed therebetween and the lumps in the kneaded object can be crushed to a certain extent.
However, this action of crushing lumps has not proved sufficient. Specifically, when the facing paddles of the two rotary shafts are nearest to each other, the object kneaded therebetween receives a pressing force, which causes the kneaded object between the paddles to escapes in the conveying direction along the incline of the paddles, depending on the nature of the material, thereby reducing the lump-crushing effect by half. In this case, sufficiently uniform kneading is no longer possible.
In the case of a batch-type kneading apparatus in which the materials to be kneaded are supplied all at once, kneaded, and discharged all at once, it is somewhat possible to adjust the degree of kneading by adjusting the operation time. In the case of a continuous-type kneading apparatus in which the materials to be kneaded are mixed while being sequentially and continuously supplied and then continuously discharged, there are limits to adjust the degree of kneading because the amount of the material supplied per unit time determines the time for which the kneaded object should remain in the apparatus (stirring time of the kneaded object). Therefore, it has been difficult to adjust the degree of kneading and perform kneading efficiently depending upon the application of the kneading apparatus.
Furthermore, a continuous-type kneading apparatus has the advantages of being small in size and capable of handling large amounts. However, in cases in which the material to be kneaded is highly fluid or cases in which the amount of the material to be kneaded is greater than the handling capacity of the apparatus, the so-called short pass phenomenon sometimes occurs in which the supplied material to be kneaded passes through the apparatus without being kneaded. This results in entirely insufficient kneading.
An object the present invention, which was devised in order to overcome such problems, is to provide a small-sized kneading apparatus being capable of efficiently performing sufficient and uniform kneading.